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18sound 18” Dual Subwoofer build
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wilidapili View Drop Down
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    Posted: 12 September 2018 at 1:45pm
Hey,

After the weekend we will start building the bass reflex cabinet design by 18sound: http://www.eighteensound.com/Portals/0/EnclosuresKits/18sound_18_dual_subwoofer_kit.pdf

It will be my (our) first speaker build. We will go as per their recommendation and use the 18TLW3000.

Here is the CAD modeled version that I made. In addition to the original picture, I added the 45* braces to the corners and a double strength baffle, as well as grooves for the baffle, "X" structure and 45* braces to sit in. Still need to decide on places for the handles. It will be built from 18mm baltic birch ply. Do you think it will be plenty strong?



The only other thread where I've seen this cabinet built is here: 
https://soundforums.net/community/threads/18-sound-design.205627/

He's done a crazy good looking job on the bracing, but seems a bit too complex for me, and I hope ours will be enough.

Will add more photos as soon as the build starts.


Edited by wilidapili - 27 September 2018 at 2:22pm
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MarjanM View Drop Down
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Points: 7702 		Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2018 at 2:34pm
You need more bracing inside, especially on the back pannel.



Edited by MarjanM - 12 September 2018 at 2:36pm
Marjan Milosevic
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wilidapili View Drop Down
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Points: 56 		Post Options Post Options   Thanks (0) Thanks(0)   Quote wilidapili Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2018 at 3:01pm
Originally posted by MarjanM MarjanM wrote:

You need more bracing inside, especially on the back pannel.

That's what I was afraid to hear. Thanks for the photo. 

I don't really know how I will achieve this. Maybe something like this...?
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Points: 1514 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Meat Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2018 at 7:23pm
Marjan is absolutely right. You need more bracing. You probably need more than your modified diagram too.

I built a low tuned reflex a few years ago with no bracing on the back panel or side panels and they resonated like crazy. Before modification it was totally unacceptable at levels 10x less than you'll be feeding that box.

The design looks pretty cool. Looking forward to seeing the build.
Don't test the champignon sound
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don't put braces exactly in the middle of panels. it will stop the lowest frequency panel vibration but do absolutely nothing to stop the next highest one. optimum positions are either 45% across the panel, or two braces at 35% and 65% across the panel.
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wilidapili View Drop Down
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Originally posted by Meat Meat wrote:

Marjan is absolutely right. You need more bracing. You probably need more than your modified diagram too.

I built a low tuned reflex a few years ago with no bracing on the back panel or side panels and they resonated like crazy. Before modification it was totally unacceptable at levels 10x less than you'll be feeding that box.

The design looks pretty cool. Looking forward to seeing the build.

Hmm okay. I think I will then try to copy the bracing as is shown in the other forum topic I linked; I think I will make the bracing exactly same, but just from 2pieces that meet in the middle with half lap joint,  so that I can cut them with my 600 x 900 CNC. 

Originally posted by snowflake snowflake wrote:

don't put braces exactly in the middle of panels. it will stop the lowest frequency panel vibration but do absolutely nothing to stop the next highest one. optimum positions are either 45% across the panel, or two braces at 35% and 65% across the panel.

This is very interesting information, thanks for this. However, I think making the bracing somewhere else than the middle will be difficult if I want to join the bracing with the ”X” -shape, since the flat piece of it is dead center... I don’t think panel vibration should be an issue with above mentioned bracing, at least the builder of that cabinet has not mentioned anything about vibration/resonance. 


Edited by wilidapili - 12 September 2018 at 8:57pm
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MarjanM View Drop Down
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Points: 7702 		Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2018 at 9:06pm
Those plans are free plans. As such you dont expect to get uber professional design that can compete with the high class manufacturer cabinets.
If it was that easy, everyone would be making those free plans and not investing in "branded" products.
Contrary to the belief, most often you dont pay only for the badge.


Edited by MarjanM - 12 September 2018 at 9:08pm
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wilidapili View Drop Down
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Originally posted by MarjanM MarjanM wrote:

Those plans are free plans. As such you dont expect to get uber professional design that can compete with the high class manufacturer cabinets.
If it was that easy, everyone would be making those free plans and not investing in "branded" products.
Contrary to the belief, most often you dont pay only for the badge.

If they provide enclosure plans for their drivers, they are meant to boost the sales of their drivers. This means they SHOULD want the cabs sounding as good as possible, so I definitely expect them to give uber professional design that makes their drivers sound as good as possible, otherwise it is just shit marketing from them to provide plans for a bad sounding, vibrating cab. 




Edited by wilidapili - 12 September 2018 at 9:36pm
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You are wrong. 
DIY market makes aproximalety 5% of the total sale. They would not like to endanger the sale of the companies that buys thousands of those drivers. They would be shoting them self in the leg.
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wilidapili View Drop Down
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Points: 56 		Post Options Post Options   Thanks (0) Thanks(0)   Quote wilidapili Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2018 at 9:47pm
Originally posted by MarjanM MarjanM wrote:

You are wrong. 
DIY market makes aproximalety 5% of the total sale. They would not like to endanger the sale of the companies that buys thousands of those drivers. They would be shoting them self in the leg.

That’s a fair point and I get that. Agree to disagree. However, not really relevant with this topic anymore.


Edited by wilidapili - 12 September 2018 at 9:56pm
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ceharden View Drop Down
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Something that would probably make a big difference would be to extend the narrow section between the ports to the rear panel.  That will tie the front and rear of the box together.

The 45deg panels in the corners will probably do little to reduce resonances.  You'd be better off with bracing going down the end panels then attaching to the ear.

You don't always need a lot of bracing, just in the right places.  The aim is to push all the resonances out of the range the cab will be used in.  In this case ~150Hz would be a good figure to aim for.

You might have to do what everyone else who design cabs does, which is to build one, find out where the resonances are, add bracing in that area and keep going til they're all high enough.

One good way of doing it is to lie the box down, put a thin layer of dry sand (or similar) on the panel then run a sine wave sweep.  The anti-nodes (points of highest movement) will show up by the sand moving away from those areas.  Alternatively my own method is just to tap the cab with a screwdriver handle etc and listen to the frequency of the resonances....

18Sound and other manufacturers provide this type of plans as an example of how the drivers can be used and are intended as a starting point, not a finished design.
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The really modern tech version would be to buy a small acellerometer of the sort used in your phone, attach to box in various places under load and turn the data gathered into a a graph of frequency vs displacement. Then use it as a sort of stethoscope to identify the worst areas that need work. This is how modern enclosures will be tested, using multiple sensors all over the cabinet.

I like the sand idea too though, that's neat and simple. Need to open and close the box which is a pita but then you would always need to when adding any extra bracing required I guess.
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